This invention relates to metering apparatus such as postage meters provided with means to provide an indication of attempts at unauthorised tampering and to inhibit operation of the meter in the event of such unauthorised tampering.
Known postage meters include mechanisms for selectively applying power to a print drum to effect printing of a franking impression on a mail item. The postage meter also includes accounting means, usually electronic, for carrying out accounting functions in respect of an amount of credit available in the meter and postage charges to be applied to mail items. Briefly, the accounting means checks to ensure that there is sufficient credit available for a postage charge desired to be applied to a mail item and, provided the credit check is satisfactory, the accounting means trips the mechanism to enable power to be transmitted to rotate the print drum through one revolution only whereby a single franking impression is printed. Usually the mechanism includes a single revolution clutch which is tripped by the accounting means so as to transmit power and the clutch is so constructed that upon completion of a single revolution of the print drum the clutch is disengaged and transmission of power is terminated. A mechanical lock prevents rotation of the print drum when the mechanism has not been tripped by the accounting means. Thus rotation of the print drum to effect printing of a franking impression is controlled by the accounting means so that printing of a franking impression can be effected only when proper accounting for the postage charge has been effected.
In other postage meters currently being marketed, the printing is effected by digital printing devices, for example thermal transfer printers.
In order to prevent, or at least inhibit, unauthorised operation of the postage meter the accounting means and, in the case of mechanical printing devices, the mechanism for locking the print drum and for selectively transmitting power to the print drum or, in the case of electronic digital printers, the electronic drive to the printer are housed in a sealed secure housing. The housing is intended to prevent unauthorised access to those components of the postage meter which are critical in controlling operation of the postage meter in accounting for postage charges and for printing franking impressions on mail items indicative of postage charges for which accounting has been effected.
Generally access to the interior of the secure housing can be obtained only by breaking the seal of the housing and hence damage to the seal indicates that unauthorised tampering has taken place or has been attempted. However attempts may be made to obtain access to components of the meter within the secure housing by making an aperture through the wall of the housing and inserting a probe through the aperture. This aperture may be of such a small size that it is not easily visually detected and hence the tampering may not be detected.